In the medicinal field, as a method for maximizing the production of proteins such as EPO with high economic-value-added, a mass production method using cell culture technology has been mainly used However, in this method, production cost is increased due to the use of animal blood as a culture medium, and expert knowledge is required for culture. Furthermore, since it is impossible to completely isolate a freshly produced EPO from an animal EPO contained in the culture medium, there is a problem in that a finally produced EPO has low purity and activity.
On the other hand, in a method for producing useful proteins using transgenic animals, a target protein is contained in body fluids secreted by the animals, so that a target protein is easily isolated and purified and maintains superior activity as compared to the existing cell-culture technology. For this reason, an interest in this method is being rapidly increased.
In the transgenic animal technology developed till now, mammary gland known to show high protein expression was mainly used as an organ for producing a target protein. However, the results of animal tests showed that it is ultimately impossible to produce several important target proteins, such as EPO, by expression in milk, due to expression in other tissues as well as the mammary gland. Furthermore, since various proteins such as albumin are originally contained in milk at large amounts, the resulting target proteins are difficult to purify.
In an attempt to overcome such problems, a method for producing useful proteins using the bladder is recently proposed.
The bladder produces urine throughout animal's life regardless of the age and sex of animals, and the urine contains protein and fatty components at only a very small amount of 5-25 mg/l. Thus, the use of the bladder makes the isolation and purification of target proteins significantly easy.
However, the protein production efficiency of animals transformed with bladder-specific promoters developed up to now is still at a very low level.
Thus, there is an urgent need for the development of a promoter, which promotes the expression of a target protein at high efficiency.